How it works: A viscoelastic material has both springlike (elastic) and dashpot-like (viscous) elements. The Deborah number De = τᴿ/t_obs separates behaviour: De > 1 → solid-like; De < 1 → liquid-like.
Maxwell (spring + dashpot in series): dε/dt = σ/η + (1/G₀)·dσ/dt → exponential stress relaxation, infinite creep.
Kelvin-Voigt (spring + dashpot in parallel): σ = G₀ε + η·dε/dt → retarded elastic creep, no stress relaxation.
Standard Linear Solid combines both: finite relaxation and finite creep, with plateau modulus G₀·α.

Left panel: 10×10 particle blob with Maxwell springs — drag to deform. Colour = local stress magnitude (blue→red).   Right panel: selected test curve (analytical) — drag the ω-slider in Frequency Sweep mode.